The present invention relates generally to provision of elastomeric tubing having utility for medical devices and particularly urethral and venous catheters. Such catheters normally are considered to be indwelling catheters in that they are placed and retained within the urethra or a vein for an extended period of time. It is well recognized that such catheters oftentimes comprise a principal avenue for introduction of pathogenic organisms.
Probably the biggest problem, and the greatest danger to the patient, that exists when using an indwelling urethral catheter, such as a Foley catheter, is infection that almost always occurs after the catheter has been indwelling for a few days. Clinical studies tend to show that the catheter, both internally and externally provides an avenue for entry of pathogenic organisms. In the former instance with respect to organisms gaining access through the interior of the catheter it is now becoming commonplace to provide means for killing organisms that would otherwise multiply in a urine drainage bag operatively connected to the catheter. In the latter instance attempts have been made to prevent organisms from entering the urethral passage between the wall of the urethra and the exterior surface of the catheter. However, such attempts with respect to providing a barrier that would prevent organisms from entering the urethral passage between the urethra and catheter oftentimes result in introducing additional problems not the least of which is increased irritation, and thus inflamation, of tissue by prior art catheters, which condition it will be appreciated materially enhances the likelihood of infection attendant the use of an indwelling catheter or the like. It will be understood that an indwelling catheter, such as a Foley catheter, is merely exemplary and that the same problems exist with respect to other drainage tubes as well as venous catheters.
Generally, prior art attempts to provide catheters intended to eliminate or minimize infection comprise catheters in which a microbiocide capable of withstanding the conditions attendant the manufacture of the catheter are actually incorporated in a composition comprising a catheter. Such catheters normally achieve a microbiocidal effect by virtue of the fact that in use the microbiocidal agents in the base material bleed to the surface and in the case of a urethral catheter result in irritation of the wall of the urethra and it is believed that catheters with such a construction are no longer in use.
A subsequent generation of indwelling catheters resorted to a somewhat different approach in an attempt to reduce infection. In this regard, and since the tubular body portion of most catheters is formed of a natural or synthetic elastomer that is hydrophobic, prior art catheters such as formed of silicone rubber have had substantially their entire surfaces, both interior and exterior, coated with a hydrophilic polymer to enable the absorbtion of aqueous solutions or suspensions of microbiocides, including antibiotics, into the coating.
In this regard U.S. Pat. No. 4,055,682 to Merrill is directed to a catheter having a silicone body portion rendered hydrophilic by contacting it with N-vinyl pyrrolidone (NVP) and exposing the catheter and NVP to ionizing radiation. U.S. Pat. Nos. 3,566,874 and 3,695,921 to Shepherd et al are representative of indwelling Foley urethral catheters made of natural or synthetic rubber and having an external coating of a hydrophylic acrylate or methacrylate polymer grafted thereto for the stated purpose of reducing irritation and infection and wherein it is indicated that the hydrophilic polymer may be impregnated with an antibiotic or germicide.
It has been found that there are severe problems encountered by both the systems of Merrill and Shepherd et al in that if a microbiocide is applied to substantially the entire surface of a catheter, in use, it will cause irritation and probably do more damage to the patient than if a standard untreated catheter were used. Further, if an antibiotic is impregnated into the surface of a catheter then only those organisms that are rendered dormant or killed by that particular antibiotic would be effected whereby the protective flora would be damaged with a possibility that other organisms normally subdued by the flora would run rampant and thus the use of an antiobiotic impregnated catheter would tend to induce rather than prevent infection.
Even more significantly it should be noted that rendering a surface of a catheter hydrophilic causes other problems. One of the most significant problems in this regard is brought about by the very nature of the coating, its hydrophilicity, that provides a wettable surface. Thus, once such wettable surface is in contact with a physiological fluid such as urine, for example, which has dissolved salts and other solid compounds in its composition, the hydrophilic coating by virtue of uptake of the aqueous moiety of such physiological fluid provides a nucleus for the accretion of salt due to a supersaturated condition adjacent the coating as well as accretion of other solid components of the composition. An unfortunate end result is a plugged catheter or a catheter with a sharp accretion of salts and the like on the exterior surface of the catheter. Needless to say in the instance of an urethral catheter having such an accretion on the exterior thereof the removal of the catheter brings about a situation not unlike the passing of a jagged kidney stone through the urethra.